Teletubbies

When my daughter was 6, she spent a morning watching cartoons, during which she saw one commercial after another for cereal, candy and cookies. Inspired by these messages, she grabbed her purse, drove to the grocery store, and loaded up the car with Cap'n Crunch, Skittles and Oreos. That was all she ate for a month.

The astute reader will notice a few hints that I made this story up: Six-year-olds do not drive, and they usually do not have access to large sums of cash. Even if they did, their parents probably would notice if they embarked upon a month-long junk food binge.

At a recent Cato Institute forum, Dale Kunkel, a University of California at Santa Barbara communications professor who wants the government to fight obesity by restricting or banning food ads aimed at children, confessed that "you could easily say, 'This is all the parents. The child does not drive to the supermarket.' " But then the conversation would be very short, and all the people who came to Cato expecting an hour-long debate would go away disappointed.

So let's set aside for a moment the question of whether parents have a right not to be nagged. Let's ask instead whether there's good reason to believe advertising plays an important role in obesity among children, who are more than twice as likely to be overweight as they were two decades ago.

Todd Zywicki, director of the Federal Trade Commission's Office of Policy Planning, noted a problem with drawing a link between fat kids and fat ad budgets: If anything, children are less exposed to food commercials than they were when they were thinner. The frequency of food ads has not increased, while kids are spending less time watching broadcast television and more time playing video games, using computers, or watching cable TV, DVDs or videotapes -- media with fewer or no food ads.

Another inconvenient fact: Places where advertising food to children is illegal, such as Sweden and Quebec, do not have noticeably lower obesity rates than otherwise similar places with different policies.

To test the plausibility of the idea that advertising has a substantial impact on weight, Zywicki asked his audience to imagine a fat child who watches six hours of Nickelodeon a day. Would you expect him to get thinner if his parents switched him to six hours of commercial-free PBS programming?

Probably not. "Watching too much TV is going to make you fat," Zywicki said, since it's a sedentary activity and people tend to snack while they watch. But if advertising had the influence its critics suggest, "the PBS diet would work."